The present invention relates to monitoring systems for monitoring individual energization of a plurality of energizable units, each connected for controlled switching of energy supplied from a common alternating voltage supply source, and for providing protection against energization of one of the units being in conflict with energization of another unit of the plurality, the system comprising a conflict detection means provided with a set of input terminals respectively connected, via individual monitor paths, to monitor individual energizable units or groups of energizable units so that respective input terminals of the set are activated in response to energization of respective individual units or groups of units, the conflict detection means generating conflict signifying information at an output thereof in response to simultaneous activation of predetermined combinations of input terminals of the set.
Such monitoring systems are already known and are generally provided with conflict protection means which are activated in response to conflict signifying information derived from the conflict detection means. Such conflict protection means may, for example, operate a relay for switching off the alternating voltage supply to all energizable units upon activation in response to conflict signifying information from the conflict detection means. Protection means for carrying out other kinds of protective functions are known and their features depend upon the character of the apparatus of which the energizable units form a part.
Although not intended to be restricted thereto, the present invention is, in particular, applicable to monitoring systems for monitoring energizable units such as signal lamps in a traffic signalling apparatus. It will be appreciated in the case of traffic signal apparatus for a road intersection employing groups of red, green and amber signals that a failure of a conflict detection means to generate conflict signifying information in respect of, for example, simultaneous energization of two lamps respectively corresponding with green signals for intersecting roadways could be dangerous. Accordingly, it is important for monitoring systems of the kind to which the invention relates to be designed for highly reliable operation and with fail-safe characteristics where practical.
For the foregoing reasons, in monitoring systems of the kind to which the invention relates it is known to operate two similar conflict detection means in parallel with each other so as to provide a safe-guard in the event of failure of one of the conflict detection means.
One known conflict detection means which may be provided is a so-called "diode matrix" comprising two sets of spaced conductors orthogonal to each other in a crossbar arrangement, each conductor of one conductor set being connected to a corresponding conductor of the other conductor set and to a corresponding input terminal. A diode matrix is able to be wired to produce conflict-indicating information in response to two given inputs of the matrix being simultaneously energized by the connection of diodes across appropriate intersecting matrix conductors corresponding with the given inputs.
Wiring a diode matrix requires the diode connections between appropriate intersecting matrix conductors to be provided by hand soldering, which is a time-consuming and costly process.
When duplicate conflict detection means are operated in parallel to improve reliability of a monitoring system, it is possible for the monitoring system to operate satisfactorily even though one of the conflict detection means is defective and the condition of the defective conflict detection means will not become known to the operators of the system until revealed by a subsequent routine manual service check of the system. In these circumstances, the failure of the remaining conflict detection means before such a routine manual service check could result in the danger of conflicting traffic signals being displayed. Routine manual service checks at frequent intervals are necessary to maintain an adequate level of protection.